English spelling often defies logic. Why should we spell ‘harass’ with one ‘r’ and ‘embarrass’ with two? Why does ‘mantelpiece’ echo its Latin origin ( mantellum, cloak) while ‘mantle’, the posh word for ‘cloak’, does not? Why does ‘dependent’ (the adjective) differ from ‘dependant’ (the noun)?
Whereas punctuation evolves, spelling does not. Whereas with grammar and punctuation you can sometimes argue a case for loose, colloquial usage, with spelling there is no way out. The word is either right or wrong — though some words are spelt in more than one way.
Nobody expects you to know how to spell all the words in the dictionary. The key thing is to avoid mistakes: learn to recognise the words you cannot spell ...