if 2 people have an cat (same address) in a box (wallet address pool of 20-100 addresses yet to be used) but cannot yet see if its an active address ready to jump out and walk around (collide and be spent by other person) or not.. ...  have they yet collided..

my point is that you can never know until you do something.

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general point to everyone

but to avoid the risks, things like random numbers/wallet seed/private key entropy should be high to avoid the chance.

assume you have the best random entropy that exists today
the chances of you choosing a specific address someone you know already has, colliding with you and/or you finding that same specific address is
2 out of 904625697166532776746648320380374280100293470930272690489102837043110636675

however the chances of a random collision with a random address is
a few million out of 904625697166532776746648320380374280100293470930272690489102837043110636675

if randomness does not produce a random factor of 75digits.. then your not grabbing a private key from the fall allotment of possible keys

EG if randomness was only between 0-200
then it will only produce 200 keys before repeating (colliding) with keys its already produced

EG if randomness was just an 8 character (alphabet only) brainwallet password
then there will only produce 208827064576 keys before repeating (colliding) with keys its already produced

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there has already been many brain wallet collissions. so yes collissions have happened and will happen
there has already been a few bad RND collissions. so yes collissions have happened and will happen

but to ensure the chances of you colliding. can be mitigated by having a 75 digit random factor to maximise the pool of addresses you can randomly land on