Your regex /(.{2,}).*\1/g will always try to capture the largest thing it can in $1. In your example string, every "b" character is followed by a "c". So every position where the string could match /b.*b/, it could also match /bc.*bc/. Since the "bc" version is longer, that's the one that will be tried first by the regex engine, and will return with success. It will never return success with $1 eq "b", even though a "b" character repeats itself in the string.

Update: it's also worth noting that m//g does not mean "try to match every possible way this match could succeed". Instead it means, "try to find one match starting at each position in the string" .. So in the above, when it matches on "bc", it will not continue backtracking to pick up the match with "b". Instead, it will be satisfied that it found a match starting at that position, increment pos, and move on.