Word or phrase for mere coincidence that brings happiness
Your exposure to (whatever) was "serendipitous" which while by definition may be about "luck", if you were not prepared for it, opportunity could have easily passed you by.
From Merriam-Webster Online Dictionary:
Serendipitous: obtained or characterized by serendipity, ex.:serendipitous discoveries
Definition of "serendipity" from Dictionary.com:
ser·en·dip·i·ty [ser-uh n-dip-i-tee]
noun
an aptitude for making desirable discoveries by accident.
good fortune; luck: the serendipity of getting the first job she applied for.