How well do you know yourself? Do you know that you have trouble saving money? Will you initially put savings in the bank, only to tap into them in a few years?
If so, read this Wall Street Journal article that explains what some smart people have done: knowing that it is difficult for them to save, they purposely choose, either in real life or in the study, to allocate funds to retirement accounts that are challenging or impossible to tap into before getting to retirement age.
All someone needs is the willpower to know how weak they are - and then ensure that they have enough for retirement by allocating their funds to accounts that do not allow early withdrawals.