The decline in Shopify's stock price following its Q1 earnings report is attributed to concerns over profitability and guidance for increased operating expenses. Despite positive revenue and GMV beats, the mixed commentary from analysts, including upgrades and price target adjustments, suggests a cautious outlook. The emphasis on marketing investments and the potential for new merchant contributions in the future adds to the complexity of predicting short-term stock movement. However, the immediate negative reaction in stock price indicates a short-term bearish outlook.