Why would the apostles die for something if they knew it wasn’t true?

A sane or mentally healthy person would not die for something that they believed to be a lie. Therefore, either they were correct in their beliefs about Jesus and in spreading Christianity, or they were insane / mentally ill.

As others have mentioned, there have been many who have died for their beliefs, even if obviously false or crazy sounding. Typically these people were not of sound mind. Of course, you could argue that believing that someone rose from the dead would indicate not being of sound mind also, so you have to look at the rest of the evidence as well.

Early writings from Christian founders do not indicate that they were out of their minds, so it would seem that they may have been on to something. Plus, it was a group of people, not just one individual. And they started a religion from the ground up, without the use of force or by the sword…

I find this to be circumstantial evidence that the Resurrection of Jesus is true.