Loss aversion is a good thing when your species evolved in survival mode, but it's not so great when you use that mindset investing. I know people who refuse to invest when P/E (or CAPE, or some other number they decided on) is above it's historical average. But a lot of those same people were too freaked out in the last crisis (where we barely even touched that) to invest anything anyway. So they just perpetually sit on the sidelines, or buy gold/hoard cash. Even a 75% crash would leave me ahead of them all at this point, and they'd probably be too scared to buy AGAIN.
That said, I'm currently trying (with new money, I have to be careful about capital gains for ACA reasons) to rebalance my international (much cheaper) vs US stocks. I'm not sure if that counts as market timing or not, but it's definitely the case that I'm not currently buying US stocks because they're so expensive (relative to international ones).
If they were both equally expensive I'd be buying them both, though, so maybe it's not timing.
-W