Other people have thought that "At the time, Russia couldn't even..." and regretted it.

Can you give some examples? I brought up Chechnya because it declared independence literally at the same time as Ukraine, and Russia waited for 3 years before finally sending the troops in (and that turned out to be a huge mess!).

Hitler mainly. Napolean? those are the classic examples. Both thought Russia was an impotent land of peasants. It's not like Russia has been invaded that many times.