He found out Wednesday in his first Grapefruit League outing.
"There was no sense of entitlement, no different from what I felt in the past, which is good," Dickey said. "I really didn't know how the security or having a spot in the rotation would affect me. When I got out there I was very competitive."
Dickey pitched three innings in New York's 3-2 loss to the St. Louis Cardinals, allowing one run on three hits and striking out four.
The right-hander retired his first seven batters before giving up three hits in the third, including a two-out RBI double by Jon Jay.
But with two on, Dickey struck out Albert Pujols for the second time. Pujols fanned all three times he batted.
"Albert's Albert," Dickey said. "One mistake and it's 4-2, so you've just got to really lock down."
Dickey is slotted to start the third game of the season behind Mike Pelfrey and Jonathon Niese. A longtime journeyman, he earned the spot after going 11-9 last year and finishing seventh in the National League with a 2.84 ERA.
"He was sharp," Mets manager Terry Collins said of Dickey's outing on Wednesday. "I didn't expect him to have his best knuckleball, but he still threw some really good ones."
Cardinals starter Jake Westbrook allowed two runs on five hits and one walk in two innings. Most important, he emerged healthy.
Westbrook, though, threw 50 pitches.
"I gave up a lot of foul balls which kind of hurt my pitch count," he said. "I got ahead and then ended up getting deep into some counts. I've got to do a better job of getting some quicker outs.
"I felt great, which is the most important part."
The Cardinals' staff has been hurt by injuries already, with 20-game winner Adam Wainwright undergoing season-ending Tommy John surgery on Monday and starter Chris Carpenter and reliever Mitchell Boggs leaving Tuesday's victory over the Marlins.
Carpenter strained his left hamstring and is expected to miss at least one spring start. No timetable has been put on his return to the mound.
Boggs strained his lower back and said he should be throwing from flat ground in a few days.
Jay was the lone Cardinal with two hits.