Why might some 20-year-olds have difficulty investing $360 per month for retirement?

Because they need the money for other necessities such as paying rent, insurance, living expenses, transportation, and even paying for college and books for college. and it’s likely they are making minimum wage if they have a job so it is hard to keep up and pay that much per month

As one myself, It’s terribly hard because I need to pay for my college which I invest 3k every 2 and a half months in, plus my rent which luckily I have roommates that help with that. Plus with the lack of time I rarely get a chance to cook for myself so I end up ordering in ( i spend probably 250$ a month on junk food) and with a pandemic going on it is extremely hard to find a job which I can balnce with my school life

Some stress reducing strategies that a lot is: aromatherapy, yoga, meditation, quiet walks in the park, or listening to relaxing music.