When the velocity and the acceleration are changing, we can define the instantaneous velocity or acceleration at any moment as the average values... … - Steven Weinberg

It is almost irresistible for humans to believe that we have some special relation to the universe, that human life is not just a more-or-less farcical outcome of a chain of accidents reaching back to the first three minutes, but that we were somehow built in from the beginning. ... It is very hard to realise that this is all just a tiny part of an overwhelmingly hostile universe. It is even harder to realise that this present universe has evolved from an unspeakably unfamiliar early condition, and faces a future extinction of endless cold or intolerable heat. The more the universe seems comprehensible, the more it also seems pointless.

A theorist today is hardly considered respectable if he or she has not introduced at least one new particle for which there is no experimental evidence.

Another lesson to be learned, to continue using my oceanographic metaphor, is that while you are swimming and not sinking you should aim for rough water.