I've lost my copy of The mathematical experience, but I recently refound my favourite quote from that book, by J. Dieudonne on the realiy of mathematics

On foundations we believe in the reality of mathematics, but of course when philosophers attack us with their paradoxes we rush to hide behind formalism and say : "Mathematics is just a combination of meaningless symbols", and then we bring out Chapters 1 and 2 on set theory. Finally we are left in peace to go back to our mathematics and do it as we have always done, with the feeling each mathematician has that he is working with something real. This sensation is probably an illusion, but it is very convenient.That is Bourbaki's attitude towards foundations

Reference and context here.