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You can't be too careful when choosing friends.
Literal
Friends [object-を] choose time [topic-は] how-much be-careful-[even-though-ても] be-too-much-[nominal-ことはない].
The idiomatic pattern いくら~してもしすぎることはない ('one cannot X too much, one can never be too X') — a stock aphorism construction. Literally 'no matter how much one X's, it's not the case that it becomes excessive.' A useful piece of formal proverb phrasing, common in advice contexts.