Unable to handle delayed gratification
Before You Begin
Pause and breathe. Even if this shouldn't be happening... accept that it is and embrace it with composure and calmness.
Calmness is the only way forward because without calm, there is no possibility for receptiveness and connection. Your child won't give to you any more than they see from you.
Never forget that a strong connection is fundamental, as there will be no correction in them if there is no connection with you.
The Core Problem
They have never succeeded in making it to the delayed larger payoff, so it doesn't feel like it will really happen.
What Will Make It Worse
Letting the child always take the immediate gratification.
What The Child Needs
To test it for themselves: Encourage the child to partake in the following experiment to decide if delayed gratification is a good thing.
Have them save up money in a Ziploc bag for a week and on the last day, give them a matching amount of money to put in the bag. Then have them start from $0 in a new Ziploc bag and save for 3 weeks and receive a matching amount to put in that bag. Finally have them repeat the same process a third time, saving their money from $0 and having you match it after two months.
At the end of the experiment, have them compare the three outcomes and decide if there was a direct link between the length of the wait to spend the money and the amount of satisfaction they got.
How To Have The Conversation With Your Child
Ask your child if they are ready to see things in whole new way.
Tell them that you want to do an experiment and no matter what, they will get extra money out of it.
Explain the experiment to them as described in "What The Child Needs" above.
Once you have their agreement, give them positive reinforcement as they save their money for each block of time.
At the end of the experiment praise their discipline and discuss the valuable lesson: In life, whether it is saving money or trying to succeed at something, the longer we don't quit and hold out while still putting in effort, the bigger payoff.
Tell them to always remember this lesson as they grow up and go out on their own.