Why three months specifically?

Long enough to see past first-date behavior (people are on their best behavior initially), short enough before attachment hormones cloud judgment. By three months, you've seen them tired, stressed, disappointed, and relaxed. You've met their friends, seen how they handle conflict, and experienced multiple interactions. It's scientifically the clarity point.

What can I assess in three months?

Basic reliability (do they follow through?), emotional stability (how do they handle stress?), values alignment (do they treat service workers well?), attachment style (are they secure or anxious/avoidant?), future vision (do they want the same things?), conflict style (can you disagree safely?). You can't assess deep compatibility on major life decisions yet.

What if I'm still unsure at three months?

That's useful information. If you're uncertain about someone who's been consistently kind and present, the issue is likely you (attachment anxiety or fear). Conversely, if you're uncertain because they're inconsistent or evasive, trust your gut—you might be incompatible or they're not ready. Don't extend past three months hoping clarity arrives.