Difference between 'at first' and 'first'

Question

As far as I understood from PEU we use at first to making a contrast with what happened erlier and later. In other cases we use just first. But I faced with the example

at first Hugo tried to be patient

there

At first was used although we didn't making a contrast. Couldn't you explain?

Answer 1

Michael Swan indeed states in Unit 84 of his "Practical English Usage" that at first is often followed by but.

But often does not mean always and does not mean in the same sentence. A contrast might be provided in a following sentence or not provided expressly and remain an implication only.

At first Hugo tried to be patient. It's easy to understand that with his fiery temperament this patience did not last.

Here, we use no but but a contrast is provided in a sequent sentence.

Answer 2

at first is used in a normal way there.

Something like...

At first, I tried to be calm and cool but then I lost my temper.

So, maybe, Hugo first tried to be patient in whatsoever situation he was in.

Answer 3

The contrast is implied in sentences such as this one. "At first Hugo tried to be patient" implies that later on he became impatient without actually stating it. If you said "At first Hugo tried to be patient but later he remained patient" it would be grammatically correct but most native speakers would be scratching their heads wondering why it wasn't stated as "Huge was patient" in the first place.