As mentioned before, one of the greatest obstacles of Imam Mahdi's advent (reappearance) is misunderstanding and superstitions in the interpretation of the term "expecting", by those who are waiting. This approach indicates that as Imam Mahdi comes, all pains and agonies will come to an end, we will find all our needs met, the sick will be healed and we will govern the whole world; which is not only a superstitious viewpoint towards the advent, but also a great obstacle. When Imam Mahdi reappears, the sincere, pure, honest shia (followers) are set to take charges in his government.
" انّ امرنا صعب مستصعب، لا یحتمله الّا ملک مقرب او نبّی مرسل او مؤمن امتحن الله قلبه بالایمان.
"Indeed our affair is difficult dealing; no one tolerates accepting it but the favourite angles or the God's messengers or a believer who Allah has tested his heart from the viewpoint of faith and belief. As evidenced by this statement, the real believers in faith would admit Imam Mahdi's Alwaite (related to Imam Ali) government. We can't expect a person to repent and have a good life after the advent, when he has sinned before, intentionally. Imam Mahdi won't reappear since the shia have this false belief in mind. (While talking about the policies of expecting, we discussed the practical ways of living and true recognition of Imam Mahdi.) The only thing some people do is crying!!! (For Imam Mahdi's occultation); while they themselves are the greatest obstacles for the advent); because this is a negative approach and a useless emotional feeling towards the advent which is not through the right path of expecting. These sorts of people just have an idea of a handsome guy (as Imam Mahdi) in mind, and naturally you will suffer in the absence of a handsome man of God and cry in missing him. Even in the era of Imam Ali's government, many shia who loved him very much, couldn't tolerate his justice and fought against him.
 Are you sure you are in a high degree of virtue at the moment and you would submit to Imam Mahdi's government at the advent time?
 This divine examination can be passed successfully when you know Imam Mahdi completely and fully comprehend the time of his advent. To be able to comprehend the time of the advent you need to be updated; i.e. you shouldn't even be satisfied with the yesterday information.
There are two kinds of expectants: 1- those who are waiting to serve Imam Mahdi.
2- Those who are waiting to fight against him.
 Why must our enemies plan their strategies based on the contemporary era but we don't make any progress? We can learn from them in this case.
From the beginning of creation, when Abel was being killed by Cain (his cruel brother), he gave the good news of coming a savior to give an end to cruelty; which is the aim of   creation. That somebody would come to complete the aim of creation. Without taking religion into consideration, indeed, in both Islamic and non Islamic world, there is the belief of a great change. We call this the advent (Imam Mahdi's reappearance). Others call it the extinction of the earth (some time in the future) or a nuclear war!!!
As mentioned before, there are different points of view towards the advent.
1- A group of people are eagerly waiting for the advent to complete humanity.
2- Another group thinks of the advent as against their own satanic purposes and are waiting to fight against it.
3- The third group is waiting for the advent to use it for their own benefits.

The real shia's viewpoint of the advent:
Shia believe that the advent is always nearby (as stated by shia scholars for centuries). This means that man is being kept between hope and fear till the advent. If Allah, the exalted, specified the advent, the expectants would despair as they would become sure that they wouldn't live till that time. So they would become disappointed to reach Imam Mahdi's government. If a shia weeps eagerly on Thursday night and more seriously tries in his personal and social life to get closer to Imam Mahdi's satisfaction, it's because he hopes that Imam Mahdi may reappear the following day (on Friday which is the promised day for the reappearance).
This type of expectation is the secret and reason of shia's activeness and dehiscence.
A true shia is the one who tries hard to do his duties to the last breath, in order to prepare and be prepared for Imam Mahdi's reappearance and government. We must have access to up to date science and technology and to further progress in these fields. Expectation is a kind of practice to increase human patience and tolerance.
It is narrated that from a hundred parts of science, only ten parts of whichhas been explored before Imam Mahdi's advent. We shouldn't be pleased that one day Imam Mahdi will come and complete science for us. Maybe that day is too late. There fore we'd better try harder each day and make more progress in different fields.
This type of expectation causes so great an activeness. Also the advent being sudden, tells the good from the bad. Like a teacher who doesn't specify the date of the exam, so that the students always be ready and waiting for it.
Not being certain about the time of the advent, the shia must always be aware and alert. From some of the signs of the advent mentioned in narrations, most of which  are indirectly stated although if God wills, all the signs will occur in a night and Imam Mahdi will come the following day.
His eminence Imam Sadiq said:
"کذب الوقّاتون و هلک المستعجلون و نج المسلمون"                                                                           
1- Whoever specifies the time of the advent is a liar. Even Imam himself doesn't know, just Allah, the exalted, knows.
2- Those hurrying for the advent would be perished. Although we should pray for the advent to approach us but we shouldn't hurry or assign a task to Allah.
3- Those who do their best will be saved i.e. those who are pious, do supplications and prayers, make progress in knowledge and are pure and sincere to satisfy Allah and his Imam to the last gasp.