This paper provides large-scale experimental and empirical evidence on the magnitude and robustness of myopic loss aversion (MLA) in investment decisions. Using a preregistered online experiment with more than 4,500 active investors, we replicate the classic Gneezy and Potters, 1997 design and show that participants who make and evaluate investment decisions frequently invest about 3.5 percentage points less in risky assets than those who make and evaluate them infrequently, smaller than prior experimental estimates. Separately, using administrative data from over 732,000 employees across 23,000 French firms, we document a nearly identical reduction in risky allocations when portfolio evaluation becomes more frequent. Together, these results refine the empirical benchmark for MLA and demonstrate its external validity beyond the laboratory. Finally, we explore whether socially responsible investments moderates this bias. Sustainability framing does not significantly reduce myopia in the experiment, and only modestly in the field. Overall, the evidence suggests that investor myopia is weaker than previously reported, yet persistent across settings, and that sustainable investments may exhibit modest resilience to short-term evaluation horizons.