5 **Why do we need mathematical proof if something is obvious?** Well, mathematicians need to be most precise and proof enables them to discover absolute truths without any shadow of a doubt (a luxury most other scientists don't have), so they set it as a standard because many things that seem obvious aren't in fact so -- for example numbers 31, 331, 3331, 33331, 333331, 3333331 and 33333331 are all [primes](prime.md) so you might think by this pattern also 333333331 will be a prime, but that's not the case because 333333331 = 19607843 * 17. Sometimes patterns deceive us, mathematicians only take proof for the ultimate solution. But indeed e.g. the industry sometimes accepts even unproven but highly likely conjectures to hold, e.g. that [P doesn't equal NP](p_vs_np.md), simply for economic reasons (the chance of being wrong is very low and profitability of being right is high).