Adjective patterns with what
Pattern 4: what v-link ADJ to-inf v-link that/whThe adjective group is followed by a to-infinitive clause.
Adjectives with this pattern indicate that something is difficult, important, or likely.
What is difficult to understand is why the army took such casualties.
In the case of important, the verb in the to-infinitive clause is often remember or note.
What's important to remember is that this information was never used alone.
In the case of likely, the verb in the to-infinitive is often happen.
difficult hard important likely
What is likely to happen is that part-timers will be drafted in.