A sunni brother mentioned:
Imam Hussein (A.S) was truthful in his determination to change the  
munkar, but he was adviced by the likes of Ibn Abbas and Ibn Umar that  
he was overoptimistic with the people of Iraq and their help. Hussein,  
being a human who is not ma3soom like the prophets, exercised his  
Ijtihad.
Based on what is even reported by the Sunnis, Imam Hussein knew that  he
 will be killed in Ashura in Karbala, and yet he went forward. Not  only
 Imam Hussein, but also all the Prophets of God knew about the  detail 
of this catastrophe. From Adam, to Noah, to Moses, to Zakariyya,  to 
Yahya (John), to Muhammad, all cried for Imam Hussein (A.S) and  
remembered him on the day of Ashura.
Imam Hussein, before he leaves Medina, saw the Messenger of Allah in dream who told him:
"Verily Allah willed to see you martyred. Verily Allah willed to see your family captives"
He knew that he will be killed where and how. There was no error in  his
 part or what you called overestimation of the people of Iraq. A  person
 who goes to a battle which has an uncertain ending, never takes  his 
family, women, and children with him, and never put their lives in  to 
jeopardy. But
Imam Hussein did all  that, knowing all the tragic events which will 
happen to them from  setting their tents on fire (by the soldiers of 
Yazid) to plundering  them and moving them from town to town. But he 
took with him women and  children because they were supposed to deliver a
 message to the people  of each town and to wake them up from their deep
 sleep. No doubt that  the event of Karbala was a turning point in the 
destiny of the religion  of Islam, by which the religion was immuned 
form annihilation.  Individuals, however, are not immune from going 
astray. But the blast in  Karbala and its inspiring effects on the 
hearts of people never let  Islam to be eradicated.
Another brother mentioned that if one knows that by going to certain  
place, he would be certainly killed, the going to that place is  
considered to be suicide, and as such, how could Imam Imam-Hussein go  
toward Karbala if he knew that he would be killed?
The above question is interesting. Imam Hussein knew where and how he  
will be killed and who will kill him. This was the case for the other  
Imams of Ahl-ul-Bayt as well. Even Sunnis narrated that the Prophet  
(PBUH) told Imam Ali who kills him and when will he be killed. But none 
 of them avoided what Allah foreordained. Thus Imams having the 
knowledge  of when they die is confirmed by both Sunni and Shia.
It should be noted that the prophets and Imams share with the rest of  
humanity the means for obtaining knowledge which Allah has given: the  
senses, the intellect, etc. They also possess special powers and means  
which other people do not have. In carrying out the commands of Allah in
  which people have also responsibility, and likewise in ordinary  
behavior, the prophets and Imams only make use of the first way of  
knowing, that is the commonly available means. The second means  
(extraordinary means) is only used by them in duties and works which are
  connected with their position of prophet hood and Imamate.
Thus in matters such as knowing the beginning of the month, passing  
judgment, finding out if something is unclean or pure, etc., they make  
use of ordinary means such as sighting of the moon, and so forth, which 
 anyone else employs. The extraordinary means of knowledge cannot be the
  basis for their action (unless in some rare circumstances when Allah  
wishes otherwise), and what they volitionally do must be determined by  
the means available to everyone. In other words, the act of Imam is  
based on the conclusion of pieces of evidences which can be obtained by 
 the ordinary human beings, and not by the information related to what  
Allah has foreordained, otherwise a contradiction would arise: For  
instance, Allah foreordained that Imam Ali be killed by Ibn Muljam (LA) 
 in the Mosque on a specific date, but since Imam Ali knows this via an 
 extraordinary means of knowledge given by Allah, if he avoids the  
Mosque, he would have gone against what Allah foreordained which is  
impossible.
Likewise, Imam Hussein  (A.S) though knew most of the people of Iraq 
will not follow him, he did  his duty by answering their unanimous call.
 Imam Hussein sent his  agent, Muslim Ibn Aqeel to Kufa, since he wanted
 to do the investigation  as an ordinary human being does. This is while
 he knew the situation in  Kufa by extraordinary means of knowledge and 
that Muslim Ibn Aqeel will  be killed, yet he was not supposed to act 
based on what is concealed  from an ordinary human being. He acts based 
on the extraordinary means  of knowledge only if Allah wishes so and 
such circumstances are rare.
Thus, such extraordinary knowledge has spiritual aspect as being the  
Representative of Allah (Khlifatullah), and the reason for it must be  
sought on this level, and it is not for the purpose of influencing and  
controlling the events on the level of ordinary understanding.
Comment : 
 Very simple explanation You do not have to go through any research just 
read Quran about scarifice of Hazrath Ismail.Did not Hazrat Ibrahim   .
 told Hazrath Ismail that he going to sacrifice him. Did not Hazrath 
Ismail was know that he will be sarified. [H2]THEN WHY HAZRATH ISMAIL 
WENT ALONG WITH HAZRAT IBRAHIM?
.
 told Hazrath Ismail that he going to sacrifice him. Did not Hazrath 
Ismail was know that he will be sarified. [H2]THEN WHY HAZRATH ISMAIL 
WENT ALONG WITH HAZRAT IBRAHIM?