Once you notice something, you start noticing it. Ever notice this? Well, even if you haven't noticed heretofore, now that I've brought it to your notice, you will doubtless start to notice that you notice things you didn't notice before once you begin to notice them.
Like the word perforce.
I bet I've gone five years at a stretch without ever thinking or seeing or using the word perforce. But in just the past week I have read it in four different places.
Now that I have perchanced to notice perforce, perforce I shall perchance to notice it again.
(And perchance you will, too. Because now you've noticed the word perforce at least SIX times already this week!)