A few habits that seem harmless but tend to cause problems later — table scraps, free-feeding, and the start of resource guarding.
Feeding from the table even occasionally teaches a puppy that hovering near people while they eat pays off, and that habit is far easier to prevent than to undo later. If you want to share food safely, put it in their own bowl rather than handing it from your plate.
Leaving food out all day is one of the most common early habits to fall into out of convenience, but it removes the routine that helps with potty training and makes appetite changes hard to notice. Scheduled meals cost a bit more attention up front and pay off in both areas.
Stiffening, freezing, or a hard stare over the food bowl is an early sign of resource guarding, even if it never escalates further. Don't test it by reaching into the bowl or taking it away. Let your puppy eat in peace, and if they're relaxed as you walk past, toss a high-value treat towards the bowl from a comfortable distance and keep walking, so people nearby predict something good. If you see growling, snapping or guarding that's getting worse, get help from a qualified professional rather than practising on your own.
A sudden switch in food, even to something objectively better, is a common cause of stomach upset. Any change is worth introducing gradually, over about a week, regardless of how good the new food is.
Relying on treats for everything can make a puppy responsive only when food is visible. Fading treats gradually as a behavior becomes reliable — replacing some with praise or play — builds a dog who listens even with empty hands.