Budget must be the first criteria but people go for arranging new fund for the reason of diversification but they should start investing from the beginning by keeping diversification in mind.
Unfortunately people come to know about diversification principal only after making their first investment (in most cases and I am talking about myself as well). For example, when people do hear about bitcoin then they will go for investing with it if they do get convinced by the potential of bitcoin and in mean time definitely they will not get time to go for studying the principles of investment which must be the problem you have notified.