First of all, let's define a father.
A father, biologically, provides his child 23 chromosomes. The mother provides her child 23 chromosomes as well, thus making 23 pairs of chromosomes. But what makes a father unique is on the 23rd chromosome set, he can give his child either the Y or the X chromosome, which determines the child's gender as being male or female, respectively. The mother on the 23rd can only give her child the X chromosome.
During this entire process, there's a lot of chromosome re-shuffling and re-combination that takes place. However, that Y chromosome is handed down unchanged from father to son, whereas the mitochondrial DNA is handed down unchanged from mother to child, regardless of gender.
If a son grows up into a man and has a baby, he is also a father. But he isn't always a dad. There is a difference. So let's define a dad.
A dad isn't perfect. Unlike a father who always hands down that Y chromosome to his son unchanged, a dad isn't always that consistent. He will make mistakes. He will lose his cool. He will make petty, unreasonable demands. But what a dad will always do is that he will always think about his children.
Even when he makes a mistake, it was trying to do what's best for his daughter or son. Even when he loses his cool, it was because he was frustrated that things didn't go right for the child. Even when he makes petty, unreasonable demands, it was to protect his boy or girl from harm.
Yes, a dad can spend a lot of time away at work. He needs to bring home the bacon. And if he's a stay-at-home dad, he can still spend a lot of time making dishes like Tartiflette from the bacon brought home. Essentially, if there's bacon, dads will spend a lot of time.
But when the bacon dealing's done, dads have a listening ear, if not a keen sense of analyzing the environment to make it better. He knows when a child is down, and so will offer to play catch outside. He knows to hold his tongue when his teenage offspring is telling him he doesn't know much about life. He even knows when to let his children fool him from time to time, allowing them to learn life's lessons themselves.
All dads want to be the greatest dad in the world. We are not humble in that one aspect. Trouble is, sometimes intentions don't always translate to actions or results. Sometimes we come close to our dream, often we fall short. That doesn't stop us dads, however, from trying. To make a day successful for a dad, it would take the strategic mind of Sun Tzu to pull it off. So The Art of War should be on every dad's library if he wants to accomplish his mission of getting his children to shout out, "You're the best, dad!!"
Therefore, the best gift a dad can receive for Dad's Day is his children's happiness. That would mean, of course, our one day of the year would turn into Children's Day. And for us dads, Children's Day is every day.