For me mistake is not strong enough, like others have pointed out a mistake is forgetting to add the yeast to the bread maker not planning, getting involved with another person (physically or emotionally) and concealing it from a partner.
Synonyms for mistake: aberration, blooper, blunder, boo-boo, bungle, confusion, delusion, erratum, false move, false step, fault, faux pas, flub, fluff, gaffe, illusion, inaccuracy, inadvertence, lapse, misapplication, misapprehension, miscalculation, misconception, misinterpretation, misjudgment, misprint, misstatement, misstep, muddle, neglect, omission, overestimation, oversight, slight, slip, slip of tongue, slipup, snafu, solecism, trip, typographical error, underestimation .