Before revision:  However, collecting sufficient calibration (e.g. trainingtemplates) data could be laborious and time-consuming, hindering the practicality in a real-world context.
After revision:  However, because of large human variability both across individuals and within individuals over time, we need to collect calibration (training) data from each individual before each session, which could be laborious and time-consuming, hindering the practicality in a real-world context.