Most of the recommendations I've seen with these funds is to just leave them be, don't even bother looking at the returns. It'll just discourage you when they dip, which they'll inevitably do at some point.
I haven't taken that advice and have checked repeatedly! But I've not cashed out because past performance over the long term (decades) suggests it'll return a decent rate. Of course, past performance isn't an indicator of future performance, but for the bigger picture passive stuff, it seems you're unlikely to lose out in the very long term.