English Standard Version (ESV)
We want to know for certain, right? As a society, we're so accustomed to being able to know that we struggle to dwell in uncertainty. It's hard for us, so we often default to certainty without actually knowing whether or not we are right. We simply default to knowing, or pretending to know, because admitting that we don't know is too hard.
Here, Gamaliel is telling the council that they don't know They don't know if the movement is of God or not, so he advises them to wait, because he's confidant that if it is not of God, it will die out, like so many other movements. If it is of God, however, opposing it is fruitless, because the will and Word of God will not be denied.
Are there situations in your life where you need to say that you're not sure? I think the world is accustomed to Christians loudly announcing how they stand on certain positions, and some of this is important. However, I also believe there are a lot of spaces where Christians need to announce that they are not sure, and they need to sit back and listen, to wait and see how the Spirit is moving, and to trust that God will make things clear. A little humility won't hurt us, and the time will allow us to discern how God is at work.