にくい

にくい attaches to the stem form of a verb (the ます-stem) to express that doing that verb is hard or difficult. It emphasizes the effort, effortfulness, or impracticality of performing the action. It is commonly used for everyday actions and skills, and is more neutral than more subjective expressions like 難しい. To describe the difficulty of actions or processes, you attach にくい to the verb stem, not to the dictionary form directly. Note that 〜にくい is not typically used with い adjectives or nouns; for those you would use different expressions like 〜くない, 〜にくさ, or other construction.