The only time that playing the same tunes becomes predictable (to our audience) is when you work a residency at a club and allow yourself to play the same stuff in the same order - in other words people get to know your routine.
Other than that, for the average punter, who may only only attend 2 or 3 family events a year, they are non the wiser.
I agree, that to us, we will find playing the same stuff very repetitive and in the case of some tracks....bloody annoying, and thats because we play it every week, or often several times a week!.
There are tracks which do work at every gig, there are also the party tracks and 70's and 80's cheese which will fill the dancefloor better than other tracks. So we tend to play it safe and stick to what we KNOW will work. If I thought that Black Sabbath - Paranoid would work at every single gig, then i'd play it, however experience dictates that at the average Wedding, Cheesier Stuff would be better received

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The Majority of the functions I do are Weddings and other Family Functions, with a median age of around 35 - 40. Thus I only play a limited selection of Chart Stuff, in favour of a broader range of 60's - Mid 90's, and for me this seems to work. However if you were doing a club or pub night, or gigs for a younger audience you'd possibly find the opposite, and that you would need a lot of Pre-Release Dance and Chart Cheese along with Commerical R'n'B.