Warren Buffett has said the best time to sell is never, and though he often doesn't follow his own rules -- as the recent sale of all the airline stocks in his portfolio attests -- it remains a good guide for investors nonetheless.

Finding good companies to invest in at the beginning means we can hold onto them for a lifetime, despite the headwinds they might encounter from time to time. The three stocks below are good candidates for the portion of your portfolio you can buy now and hold onto forever.

Pocket watch on $100 bill

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AbbVie

Two factors have typically informed an investor's decision to buy pharmaceutical giant AbbVie (NYSE:ABBV): its healthy dividend and its arthritis treatment Humira, one of the best-selling drugs of the past two decades.

The annual dividend of $4.72 per share yields 4.9% and remains as safe as ever -- even during the pandemic, when other companies have cut or suspended their dividends, AbbVie's payout remained intact. It has even increased the dividend by more than 130% over the past five years.

Humira has had a long, prosperous run, but even AbbVie realizes the clock is ticking on its exclusivity and it needs to protect itself from over-reliance on the treatment. Its pipeline of therapies remains vibrant, however, and just recently the pharmaceutical announced positive results from its phase 2a clinical study of potential Humira successor ABBV-3373 for the treatment of rheumatoid arthritis, which has been colorfully described as "Humira on steroids (literally)." 

AbbVie also just inked a deal with Genmab (NASDAQ:GMAB) for $3.9 billion to jointly develop and market three oncology therapies, indicating the pharma is ready to face the market challenges for decades to come.

3M

3M (NYSE:MMM) gained a lot of national and global prominence during the COVID-19 pandemic because of its production of N95 masks and respirators that were essential protective equipment for healthcare and other front-line workers. 

Yet the company that got its start back in 1902 mining minerals for abrasives (3M stands for Minnesota Mining & Manufacturing) now makes products for virtually every industry, from automotive and electronics to construction and consumer products. It's those latter items that most people are probably most familiar with, such as its Post-It Notes, Scotch Brite cleaning pads, and Scotch tape.

The diversity of industries it serves and its global footprint offer investors a bit of downside protection in the event any one business or region falters, though in a global pandemic even that's not enough. Not even making essential PPE nonstop could offset the decline it experienced in its other segments this past quarter.

Still, 3M has been through numerous global calamities and business cycles over the last 120 years, and for that reason it has become an income investor favorite, having raised its dividend every year for over 60 years, making it a part of that rarefied group of companies called Dividend Kings. 

There's good reason to believe 3M's broad diversity will continue to serve it and investors well for another lifetime and beyond.

Sysco

During the coronavirus outbreak, food service leader Sysco (NYSE:SYY) learned it had a blind spot in its business: Its laser-like focus on restaurants, educational institutions, and hospitality businesses meant it was at risk if all of those businesses were simultaneously shutdown.

Now, having a global pandemic to suddenly knock virtually the entirety of Sysco's business offline is not something anyone anticipated, but it did open the company's eyes to the fact it needed to expand its field. Sysco and industry peer U.S. Foods (NYSE:USFD) are now looking to break into supplying supermarkets with food. 

It won't be easy, as grocery stores already have their own supply chains -- but even the supermarkets found those chains broken at times, and may find having yet another outlet available is a smart decision.

The economy is reopening, so the collapse in business Sysco experienced ought to reverse, particularly as restaurants and other kitchens look to restock after a three-month hiatus. 

One thing hasn't changed for Sysco, and that's its dividend, which like 3M's has remained intact for decades as the company has increased the payout for over 50 years. It has returned almost 20,000% to investors over that period, compared to a 2,700% gain for the S&P 500, and it's not unwise to believe its record of outperformance will continue for many more years.