As you farm and mine in Story of Seasons: Pioneers of Olive Town, your stamina will be the only thing that really limits you every day.
However, you can increase your stamina by six more hearts, allowing you to do more. To do this, you’ll have to meet the Harvest Spirit, which happened after we collected 100 Follower Sprites and entered Olive Town. You can find Follower Sprites while doing many different actions like mining, farming, and woodcutting, just to name a few. We had 100 by the beginning of summer.
At the shrine to the north of town, you can spend your sprites on upgrades, including upgraded soil for your farm and access to new magical areas. The first stamina upgrade will cost 10 Sprite Coins, and the price ramped up until the final upgrade, which costs 60 Sprite Coins.
If you have found 100 Follower Sprites but the Harvest Spirit isn’t appearing, make sure you’re going into town frequently, as that often triggers required cutscenes that need to occur before she shows up.