I'm no expert either but I believe Timbo is right. Lightning is an instantaneous discharge of static electricity that builds up in the earth and flows skyward. Everyone thinks it's a "bolt" from the skies and that it "strikes" something on the ground but I don't think that's actually right. Static (electrical potential) builds up in an area on the ground and when the potential difference is high enough to overcome the resistance of the air the potential difference discharges and everything that is electrically connected in the area (ie earthed) discharges with it. If you are earthed and standing near something that is not earthed or vice versa then whatever is earthed will experience the sudden discharge of the lighning while whatever is not earthed will remain with the static charge until it gets too close to something that is earthed or something that is earthed gets too close to it. I'm not sure if I'm making sense but the charge builds up slowly everywhere and discharges instantaneously in things that are electrically connected, leaving some residual charges behind which discharge through earth as they can - ie someone who is not earthed and is charged up touching a boat that is not earthed and has discharged or vice versa?