Maths makes the decision obvious. Suppose you invest two quid every day at the reasonable rate of 10%. It will take you almost exactly 50 years to accumulate £1m. To earn this same £1m in the National Lottery, you would (on average) have to match five numbers and a bonus ball, at odds of 2,330,635-to-1.
If you spent two quid a day for 50 years you would total just over 36,500 tickets and would thus have only a 1-in-63 chance of making that million pounds. However, the available image of immediate wealth subverts this rationality.