What are good reasons to postpone an engagement proposal?

What are good reasons to postpone an engagement proposal?
I was thinking about proposing to my girlfriend by Christmas or around it, but some recent events made me reconsider and postpone it by some months even though I already got the rings. First I want to take care of some business, although the biggest issue is already settled.
I think she's expecting the proposal and maybe even found the rings (maybe, I really hope not - I hid them in a safe place today) but that's not going to happen now or anytime soon. Should I tell her something?
Updates
+1 y
Just to make it clear - I got two rings instead of one because here both the engaged people ("fidanzati") wear one, not only the woman.
Updates
+1 y
Since I have a reasonable suspect she found them and has gotten quite vocal about the topic of commitment, I'll probably make the proposal tonight.
What are good reasons to postpone an engagement proposal?
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