Focus at work is increasingly difficult due to constant interruptions from tools like Slack and Teams. Paul Graham highlighted this issue in 2009, and the pandemic has exacerbated it. The article uses mathematical modeling to explain how interruptions impact productivity. It identifies three key factors: λ (lambda), the rate of interruptions; Δ (delta), the recovery time after each interruption; and θ (theta), the minimum time required for meaningful work. Understanding these parameters can help individuals assess their focus and productivity levels. One example illustrates a "lost day" with only 3 hours and 58 minutes of focus time, hindered by 19 interruptions that cost 242 minutes of potential productivity. In contrast, a "good day" yielded 6 hours and 14 minutes of focus time with fewer interruptions. The article emphasizes the importance of minimizing interruptions and maximizing uninterrupted work blocks to enhance productivity. The capacity for real work is calculated based on these factors, demonstrating how small changes in interruption rates or required focus times can significantly affect overall output. The article also outlines how to simulate multiple workdays under consistent conditions to better understand productivity trends. By modeling 100 days, one can gain insights into how different environments and work habits affect focus over time. This approach shifts the conversation about productivity from vague complaints to a more analytical understanding, allowing for targeted improvements in work habits.