There would still be eyewitnesses around when the first letters were written even if the stories weren't being told by those who were witnesses which is most likely the case.
Funny how there are no records of these eyewitnesses.
The guys that got involved in this dedicated their lives to it which I can't see happening if they weren't convinced of the truth of the resurrection. In addition the faith grew rapidly and sustained that growth which I can't see happening if the resurrection is just a fable.
Your incredulousness has no affect on reality.
There have been lots of times lots of people have believed things that were not true.
There are other threads to hash this out.
Facts don't lie or have an agenda. Facts are just facts