Even moreso . I like the Rob Pike restatement of this principle, it really makes it crystal clear:

"You can't tell where a program is going to spend its time. Bottlenecks occur in surprising places, so don't try to second guess and put in a speed hack until you've proven that's where the bottleneck is."

Moreso, in my personal experience, I've seen a few speed hacks cause incorrect behavior on more than one occasion.