Non-Disclosure Agreements are necessary because there are legal issues that occur without one. For example, sharing your project without an NDA may cause you to lose your trade secret or patent rights.
Sadly, having a handshake agreement or “friend-D-A” does not solve the problem, either.
There is a domino effect with NDAs. Virtually all NDAs require that something be kept secret *unless* the person makes the information public. We don’t want someone to trigger that domino effect by inadvertently sharing their information with someone else.
You can learn more from this topic taken from the (free) Ethical Collaboration Certification training: http://ethicalcollaboration.22.214.171.124.xip.io/topic/friend-d-hurt/.