Shares of advertising technology company The Trade Desk (NASDAQ: TTD) have soared this year. Indeed, the best description of the company's year-to-date stock chart is up and to the right. In total, the growth stock has approximately doubled during this period. With such strong gains in the rearview mirror, is it time for investors to sell and make their big win permanent?

When I asked this same question in early June, I argued that shares were worth holding onto despite their 66% year-to-date rise. But with the stock already gaining more than 21% from those levels, it's time to revisit this question.

While it feels great to have a big winner in your portfolio, investors should be sure to remain objective. There's no way around it: a stock becomes less attractive when its price soars higher in a short period of time without any new information suggesting shares are worth materially more than they were at the start of that period. In other words, the risks to owning a stock increase when the valuation becomes more speculative.

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Source Fool.com