This is a common fallacy, that investment confers some sort of validity. It doesn't. It means only that Sequoia et al. think Y Combinator's model will work. The

This is a common fallacy, that investment confers some sort of validity. It doesn't. It means only that Sequoia et al. think Y Combinator's model will work. They don't have a crystal ball, and the model is no more or less likely to work than if they found $2m on the side of the road. I've thought it will work (for them anyway, not for many of the competitors) since before I went through it, but I don't really consider this validation of my belief.