When the particles て and は are combined, they form a regular composite structure that is used primarily to highlight repeating actions, or to make assessments or judgments about potential situations. In this grammar structure, we will be looking at the nuance that is used with potential situations. This may be interpreted simply as ‘if (A), (B)’, ‘when (A), (B)’, or ‘because of (A), (B)’.
At times when used as ‘if’, ては will generally express some sort of negative expectation or comment.
Depending on what ては appears after, では may be used instead. This is the case when following nouns, な-Adjectives, or verbs that require で to be used instead of て when conjugating.

• そのように力（ちから）を入（い）れて回（まわ）してはネジがだめになってしまいますよ。
  If you turn it with such force, you are going to ruin the screw.
• そんなに長（なが）くては鞄（かばん）に入（はい）らないので、半分（はんぶん）に折（お）ってください。
  If it is that long, it won’t fit into my bag, so please fold it in half.
• 私（わたし）は掃除（そうじ）が苦手（にがて）なので、そんな几帳面（きちょうめん）では私（わたし）と住（す）むことができないだろう。
  I don’t like cleaning, so if you are that well-organized, you probably won’t be able to live with me (you probably won’t enjoy living with me).
• そんな貧乏（びんぼう）くさい格好（かっこう）ではあのレストランには入（はい）れないよ。
  If you have such a poor-looking outfit, they will not let you in that restaurant.

As with many other structures that use ては or では, it will often be shortened to じゃ or ちゃ.

• リーダーがあの人（ひと）じゃ嫌（いや）です。どうしてもあの人（ひと）じゃないといけないなら私（わたし）を別（べつ）のチームに入（い）れてください。
  If that person is the leader, screw that. If there is really no other way than making that person the leader, then please put me on a different team.
• ご飯（はん）を全部（ぜんぶ）食（た）べなくちゃ大（おお）きくなれないよ。
  If you don’t eat all your food, you won’t grow.