Many of the senior Crossrail team had spent time doing the JLE hence the invincible we can do it type attitude.That is also true and probably played a significant part.
The reality was they made the 2000 deadline by ditching the planned new signalling system and everything ended up getting resignalled 11 years later.
This not being a sensible option on Crossrail as there are delays on other critical paths so pushing on is key.
In the end they didn't learn a key lesson from JLE - leave enough time for system integration