〜やすい and 〜にくい: easy or difficult to do
Attach these endings to a verb's masu-stem to describe ease, difficulty, or a tendency for something to happen. Read them separately from expressions of ability.
Attach them to the masu-stem
Remove ます from 読みます to form 読みやすい, and from 運びます to form 運びにくい. With します, use しやすい and しにくい.
取っ手が付いているので、この箱は運びやすいです。 says this box is easy to carry because it has a handle. Look for what makes the action easier.
Evaluate the situation or a tendency
この手袋をしたままでは、細い糸を結びにくいです。 means that tying a thin thread is difficult with these gloves on. にくい can describe a difficulty caused by a tool or situation, rather than just a person's skill.
この容器は落としても壊れにくいです。 describes a container that does not break easily even if it is dropped. やすい and にくい can also describe how readily an event occurs, including events that are not intentional.
Distinguish difficulty from inability
この言葉は発音しにくいですが、練習すれば言えます。 says the word is difficult to pronounce but can be said with practice. にくい does not by itself mean the action is impossible, as 発音できない would.
In forms such as 読みやすかった and 読みにくくない, the final やすい or にくい conjugates like an i-adjective. Tense and negation appear on that final element.
Quick check: Does このボタンは押しにくいです。 mean that the button cannot be pressed?
Show the answer and why
No. It says the button is difficult or awkward to press; the sentence alone does not establish that pressing it is impossible.