One of Sitecores features is the ability to assign profile cards or profile key scores to pages. As visitors browse the website the profile key scores from each page are added to the visitors profile. Visitors are then assigned a pattern card using N-Dimonsional Euclidean Distance to calculate the closest matching pattern card to the visitors profile.
However before a pattern card is assigned to a visitor they must visit a minimum number of pages. The default for this is set to 3.
Reasons for changing this could be that you actually want to be more certain of a users profile before triggering personalisation this could be to avoid visitors landing pages on the site heavily dictating which persona they initially become profiled as, which in turn could influence personalisation that keeps them in that persona.
Or it could be because you want to lower the number of pages for a more immediate effect.
Whatever the reason to change the default from 3 you need to add the following setting to your config:
<setting name="Analytics.Patterns.MinimalProfileScoreCount" value="3"/>