Is there a point, if ever, where you need to reevaluate your original thesis?

Everyone says to invest in something you believe in and don’t look at it. But is there any point at all during which you really should reconsider whether you made the right decision initially? Even though you might have thought long and hard about, did extensive research about and came up with a solid thesis about one stock before investing in it, sometimes blind belief in your original thesis isn’t the way to go if you’re down 25%.