"Never try something new before a big ride or race."
The classic for me is the time a buddy entered a race at a nearby snow ski area that held XC races there in the summer. He was a really strong rider and regularly kicked butt on anything that went uphill, only topped by the very young and Expert/Pro level racers in our group.
He would have been an amazing SS rider, but no one was doing that then that we knew, back in the 90's.
Race day comes and he is a nervous nellie for some reason and must have felt he needed some kind of 'edge' that morning. He borrowed a package of sports drink, mixed it up in a bottle, and began the race. DNF. Stomach cramps.
Maybe it was mixed too strong, or maybe it just did not agree with him bio-chemistry wise. Dunno. But he made that glaring error to try something new and unproven the 'Day Of' a big event.
When I try a new part or product, I always give it a spin around the local hills first before I jump into some epic ride only to find that it...well in the parlance of Texas, that is either "sticks, stinks, or stings". Seems like most things in the Lone Star State do one or the other (or all three).
That is why I never try something new on a big ride without testing it a bit first and also why I don't ride in Texas.