please increase my TEMP Tablespace

Today I recieved a call. I was asked to increase a TEMP Tablespace as it was 100% used. I checked the TS and it was correct - 100% full. So I added additional 10% to the tempfile.
So what?
It's only fighting symptoms.
After some minutes I got the same call again.
I suggested the Apps responsible to check the statements or response time. After some minutes he agreed. Because of some new analyses some plans flipped. This caused some more scans and in memory sorts than necessary, which landed in Temp TS.
The solution was obvious: change the objects stats back to 'good' values.
The learnings: once again: don't fight symptoms. It will bring you to no end. Find the initial cause and fix it.