You can misspell any word, at any time. All it takes is a slip of the finger, and 'rain' becomes 'rayn'. Some words, though, attract errors the way a black sweater attracts lint. Memorise these 'devils' so that next time you want to write one, you will place each letter where it belongs.
Here is a list. First you see the spelling word. Next is the definition. Last is what you should remember, so you can spell the word correctly.
embarrass 'to make someone feel shame' Remember: double r, double s
argument 'disagreement' Remember: no e after the u
beginning 'start' Remember: double n
committed 'pledged to' Remember: double m, double t
deceive 'to trick' Remember: i comes after e, when both follow c
conscience 'inner guide to right and wrong' Remember: science is part of the word, with an s and a c
business 'store, company, work' Remember: an i comes before ness
February 'second month' Remember: an r comes before u
dependent 'relying on someone or something' Remember: ent, not ant
despair 'hopelessness' Remember: des, not dis
separate 'apart' Remember: pa, not pe
disappear 'vanish, go away' Remember: one s, double p
forty '40' Remember: no u
grammar 'the structure of a language' Remember: ar, not er
knowledge 'information, awareness' Remember: dg, not just g
eighth '8th' Remember: add h to the word eight
laboratory 'science workroom' Remember: o before ra
jealous 'envious' Remember: ea, not e
exaggerate 'make bigger, stretch the truth' Remember: double g
excellent 'great' Remember: ent, not ant
success 'achievement of a goal' Remember: double c, double s
definite 'fixed, certain' Remember: i, not ate
original 'the first, unchanged' Remember: nal, not nel
sincerely 'honestly' Remember: ely, not just ly
weird 'strange' Remember: ei, not ie
weight 'heaviness' Remember: ei, not ie
whether 'expressing a choice between two things' Remember: wh, not just w
therefore 'thus, so' Remember: ends with an e
all right 'all acceptable' Remember: two words, not one
Many more spelling devils could appear here. As you notice words you often misspell, add your own personal 'devils' to the list.