ВОЙДИТЕ, ЧТОБЫ НАЧАТЬ ОБУЧЕНИЕ С АУДИО-ЗАПИСЬЮ

Grammar II - 18.02

~てしまう - ~te shimau

  The te-form of a verb + しまう has two senses, which at first might appear rather incongruous.
  In its first sense, shimau indicates that one "carries out with determination" a plan described by the verb.
It typically involves bringing something to a culmination point.
You, in other words, do something completely, or finish doing something, or have something done.
本を読んでしまいました。 I read the book completely./ I finished reading the book.
hon-o uonde shimai mashita.  
  The second sense of shimau is "lack of premeditation or control over how things turn out."
This often comes with the sense of regret; something regrettable happens, or you do
1 something which you did not intend to. (* 1)
電車の中にかべんを忘れてしまいました。 I inadvertently left my bag on the train.
densha-no naka-ni kaban-o wasurete shimai mashita.  
  *1

Since shimau goes with the verbal te-form, which is affirmative,
it only gives us sentences meaning that something regrettable does or did happen.
In other words, we cannot express with shimau negated ideas such as
"regrettably, x did not take place" or "unfortunately, I did not do x."

   
宿題を忘れたので、
先生は怒ってしまいました
To my horror and sorrow, my professor got angry, because I had forgotten my homework.
shukudai-o wasureta no de,
sensei-wa okotte shimai mashita.
 

  Both senses focus on the discrepancy between what we intend and what the world is like when it is left on its own.
A shimau sentence may be ambiguous between the two senses.
How a given shimau sentence should be interpreted depends on the assumptions the speaker has when uttering it.
For example, the "finished reading" sentence above
can be read in the "regrettably" sense equally easily
  if you read the book although you had not planned to,
  or knowing that it was wrong but unable to resist the temptation.
   
  In speech, ~te shimau and ~de shimau are often contracted
to ~ちゃう - ~chau and ~じゃう - ~jauu respectively.
宿題をなくしちゃった I lost my homework!
shukudai-o nakushi chatta.  
   
食べてしまいますー>食べちゃいます

he ate (to the end, finished fully)

tabete shimai masu - tabe cha imasu

 
死んでしまったー>死んじゃった he died
shinde shimatta - shin jatta