Mark Sletten wrote:

"The second manual, lets call it our REGS (sorry again), tells us IF we can
operate the aircraft.  If the crosswind doesn't exceed 15 kts, if the
ceiling is above 1000', if... whatever.  Create a Minimum Equipment List
(MEL) and put it in your REGS.  Set your minima according to an honest
evaluation of your capability then, and this is most important, STICK TO IT!
A quick review of the REGS prior to flight can help make safer go/no-go
decisions."

I think this is a good idea and would add a section that had to do with when to turn back, once in the air.  I think a lot of bad judgments are made after a reasonable takeoff decision but when it turns out that the conditions are worse than expected.

A couple ideas that help me:

1.  I will happily file IFR with at least 500' ceilings and no significant risk of ice or convective activity.  When either either ice or serious convection are present, I may still go but only if I can remain VFR.  If I can't, I'm on my way back.

2.  Whenever I try anything that I am not sure is going to work, I use the 99% Plan B rule.  I am ok with trying to fly a plan that has a 30% chance of working out as long as I always have a Plan B that is 99% sure to work.  What that plan is (and whether there is one) can change from minute to minute (for example, always having an airport you know you can make but the airport keeps changing) but at any point if I think I am about to lose my 99% Plan B, Plan B becomes Plan A and that is what I do.

I think some weather related accidents occur when unexpected conditions crop up and the pilot has no process that he/she has thought out in advance for how to decide what to do about it.