Add three hours, and remember the day is already half gone
Pacific to Eastern is an addition of three hours on every date of the year, since both zones observe daylight saving on the same schedule. The arithmetic is trivial; the scheduling consequence is not.
By the time the West Coast starts, the East Coast is at lunch
A 9:00 AM start in Seattle or San Francisco is already noon in New York. Anyone on the East Coast has had a full morning, and their afternoon runs out at 2:00 PM your time. This is why West Coast teams working with East Coast counterparts tend to front-load: calls before 11:00 AM Pacific, asynchronous updates after that. Booking anything at 3:00 PM Pacific means asking New York to stay until 6:00 PM.
Market and broadcast hours
The New York markets open at 9:30 AM Eastern, which is 6:30 AM Pacific, and close at 4:00 PM Eastern, or 1:00 PM Pacific. Live television and product announcements quoted in Eastern land in the West Coast morning. If you are on the Pacific side, most of the national calendar happens before your afternoon.
Strict PST versus Pacific local time
Strictly, PST is UTC−8 and only applies from early November to mid-March. For the rest of the year the West Coast is on PDT at UTC−7. Because Eastern shifts on the same dates, the three-hour difference between them is unaffected either way. The distinction only bites when converting to a zone that does not observe daylight saving at all.