Many of us have seen the famous marshmallow test. Put a kid in a room with a marshmallow in front of her. Tell her that if you're leaving for a few minutes, and if she waits for you to return without eating the marshmallow, she'll get another one. The results are pretty comical (and agonizing for the kids), as this popular Youtube video shows.
The initial study was done in the 1970s by Walter Mischel at Stanford University to study when the control of delayed gratification developed in children. In follow up studies, he unexpectedly found a correlation between the children who were able to defer gratification and their success many years later. Parents described them as significantly more competent adults, and they exhibited higher SAT scores.
The concept of delayed gratification is linked to inhibitory control - one of the key components of executive function which develop in the critical 3-5 year window for young children. Inhibitory control itself is comprised of response inhibition (which this experiment measures) and distraction suppression. Both of these skills are critical in terms of developing patience, self-regulation and avoiding distractions while focusing on a goal. Hence it's unsurprising in hindsight that the simple marshmallow test could be a good predictor of a child's eventual success.
What are some of the ways we can cultivate this skill early on? Praising a child for showing good "waiting skills" (or patience) is one. Playing turn-based games is another. When children have to wait their turn, they are practising restraint and controlling impulses. Having them put in effort for or work towards a reward later on is a good one. What are some other ideas you have tried?