This is such a good post and advice!

And it applies to any type of troubleshooting; from trimming and radio and tunning problems.

Assumptions are the big obstacle for proper and fast solutions; yet, are very common.

One unknown variable changes, and the output changes.
By assuming that other variables have gone wrong (may be is this, may be is that....) and proceeding to modify one after the other, the only result is that a bigger problem than the original is created.

It takes experience and careful analysis to determine what is the variable that has changed and why.