Al Horford left the Celtics in free agency once. He had no interest in doing so a second time.

That, Horford said, was the biggest reason he agreed to a two-year, $20 million extension Thursday to remain with the Celtics through the 2024-25 season.

"For me, I really did want to be a part of what we have going here," Horford said after the Celtics held a shootaround at their practice facility ahead of Friday night's game against the Miami Heat. "I felt like me coming back here last year, I felt the strides the group started to make and we've continued to make strides in the right direction.

"I feel like there's a real purpose of trying to win and the group that we have is just a really good group. So, I'm happy and we know we have a lot of work ahead. But this type of stability, it's hard to find."

Horford learned that the hard way. In 2019, after spending three seasons in Boston -- and reaching the Eastern Conference finals twice -- Horford chose to join the Philadelphia 76ers on a four-year, $109 million contract, the final year of which Horford is currently playing under.