In the early 70's Stan (The "S" in PS) and I only made phono preamplifiers. They had no controls, just a turntable input and a set of RCA outputs. Designed to go into the auxiliary inputs of the user's preamplifier. But that was never how we used it.
It was impossible for us to design good phono preamplifiers with another manufacturer's preamp - because we'd be tuning the sound of the phono stage to work perfectly with one preamp - and that preamp wasn't ours. Pretty tough to tell customers they'd have to buy an Audio Research SP3 to get full benefit of the PS phono stage. We used only a potentiometer (called a Pot) into the power amp because our phono stage had plenty of gain - but most importantly it didn't color the sound of the phono stage.
When it came time to acquiesce to customer demands for a full PS preamplifier, which traditionally consisted of a phono preamp a pot and a line stage, Stan and I started to design one - only to discover we couldn't make a line stage that didn't both add and subtract from the sound of just the pot into the amp. We tried every circuit we knew how to make but they all colored the sound somewhat. Neither of us were willing to give up the purity of the pot going straight into the amp. We were stumped.
Stan came up with the answer. "Let's do both!" He said.
"Both?" I asked what he meant.
"Just add a switch on the front panel. In one mode you'd have just the output of the pot into the amp like we have now. In the other mode you'd get the output of the line amp for the guys that need the extra gain."
And thus the switchable concept we pioneered of "pots in a box" or not - later called "Straightwire" was born - all because we were unwilling to compromise the sound.
I wonder how many concepts we take for granted were born out of this very same process?