Infinitive clause as subject

An infinitive clause can be the subject of a sentence. This was common in older English.

To err is human; to forgive divine.
To find fault with others is easy.
To make mistakes is easy.

In modern English infinitive clauses are rarely used as subjects. We more often use it as a ‘preparatory’ subject and put the infinitive clause later.

It is easy to find faults with others.
It is easy to make mistakes.

Infinitive or gerund?

To talk about an activity in general we often use an -ing (gerund) structure at the beginning of a sentence, rather than an infinitive clause.

Selling insurance isn’t easy. (More natural than To sell insurance …)
Teaching kids is a rewarding job.

Infinitive clause as complement

An infinitive clause can be used after be as a subject complement.

My ambition was to become a pilot.

Sentences like these can also be constructed with preparatory it.

It was my ambition to become a pilot.

Infinitive clause as object

Many verbs can be followed by an infinitive clause in the place of the direct object.

I like eggs for breakfast. (Noun object)
I like to have eggs for breakfast. (Infinitive clause as object)

The verbs that can be followed by an infinitive include the following:

afford, agree, appear, arrange, ask, attempt, bear, beg, begin, care, choose, continue, dare, decide, expect, fail, forget, happen, hate, help, hope, intend, learn, like, love, manage, mean, neglect, offer, prefer, prepare, pretend, promise, propose, refuse, regret, remember, seem, start, swear, trouble, try, want, wish