All too often, I come across someone who says the rather stupid expression, "You gotta do your due diligence before you buy." Stupidly, many who say such, believe, wrongly of course, that doing your due diligence means researching an investment or speculation before buying.
You can't do your own due diligence. You can't owe yourself any legal requirement to consummate a deal.
Due diligence is what one party owes another party because of legality. Due means that which is owed. Diligence in the context of due diligence means a best effort of the facts presented so as not to commit fraud in a commercial deal.
Would-be sellers of things that have legal requirement of prospectus owe a best-effort to present the facts. Those offering stock for the first time, those offering realty and so on have requirement by law to disclose pertinent facts.
They owe (due) a best-effort (diligence) to give the facts to would-be sellers.
Legislators either have written law directly or have given authority to regulators who require legally-mandated documents, which disclose essential facts. Preparation of these documents must be done with earnest to present the facts so as not to commit fraud.
Many get confused because the words due and do are homophones. It's a linguistic error made by many that has arisen since the boom days of the Internet IPO by neophytes. The frequency of the error has risen quite a bit in the last ten years, especially in the latter days of the housing bubble.
Likely, wily advertisers have misled many into the idiotic belief that due diligence means comparison shopping. It doesn't. As well, it doesn't mean shop around nor compare prices, nor research before you buy.
Advertisers have done their best to wreck English. These days, it's common to hear or read in advertising the word ridiculous to mean amazing rather than what it means, that which is excites laughter from derision. It sure is ridiculous that too many say due diligence to mean comparison shopping.
If someone says to you, "You need to do your due diligence before you buy," run! Do not listen to them! They don't know what they're talking about.
Ordinary, average guys never make such mistakes. Instead, they hope their doo is hard.