When a man does not know what harbor he is making for, no wind is the right wind. – Seneca

A quote by  Lucius Annaeus Seneca (a.k.a. Seneca the Younger, 4 BC–65 AD) a roman philosopher, statesman and more.
I think a form of this quote might have been used literally at some stage, then Seneca adopted it in it’s philosophical meaning.

When a man does not know what harbor he is making for, no wind is the right wind.

Seneca

My opinion:

This quote carry a great idea that is essential to success, having a goal. Having a goal is key to success, without a goal to work for, time is wasted.

When a man does not know what harbor he is making for: When a person does not know where he is heading. Does not know what he wants.

No wind is the right wind: No path is the right path. No offer is the right offer.

The quote probably means that without having a goal you will not be able to catch the right opportunities.
Or another possible meaning, a project with no concrete end goal will fail.

Given that a lot of people just cruise through life with no real goal or purpose, especially after failing to achieve their childhood goal. These people fail to catch opportunities, because they have not set a new goal.

Having a purpose or a goal is a very important subject, that Seneca addressed 2000 years ago …

You can read this article about how to find a purpose or goal.