The book says: being first in the market is better than having a better product than a competition.
Examples: we all remember who first flew over Atlantic or who was the first man on the moon but almost no-one knows who was the second.
Heineken was the first imported beer in USA and still is No. 1 imported beer.
Same for Miller Lite, first domestic light beer.
Being first doesn’t matter if the idea/product is not good.
I think it’s better to say that being first gives one extremely big advantage over competition but doesn’t guarantee the success.
It’s rather obvious that it doesn’t matter that you’re first to market if no-one needs your product or if your product is very bad.
There are many examples from computer industry that disprove this rule (i.e. first spreadsheet isn’t the dominant spreadsheet, first word processor isn’t the dominant word processor) so there are (many) cases showing that n-th product can overtake early leaders.
But it’s very hard and usually requires the leader to make huge mistakes.
See also Eric’s take