This technical blog post provides a comprehensive overview of the Internet of Things (IoT), demystifying its core concepts and architecture. It explains how IoT bridges the physical and digital worlds through interconnected devices, gateways, service applications, and servers. The post emphasizes the importance of IoT for individuals, businesses, and society, highlighting its potential to enhance convenience, efficiency, and sustainability. The author explores essential IoT components, including end-devices, gateways, servers, and service applications, detailing their roles in sensing, transmitting, processing, and acting on data. It also addresses common misconceptions about IoT, clarifying that it extends beyond smart homes and involves multidisciplinary systems. The post further discusses network topologies like direct connections, hierarchical connections, and mesh networks, explaining their trade-offs in terms of power, scalability, and resilience. Additionally, the author delves into non-IP connection technologies, such as UART, CAN, IEEE 802.11, Bluetooth/BLE, LoRa, and GNSS, and application protocols like LoRaWAN, MAVLink, UAVCAN, NMEA/UBX, Thread, CoAP, MQTT, and LwM2M. The post also covers Firmware Update Over-The-Air (FUOTA) and IoT security, emphasizing the need for cryptographic foundations, secure communication, secure boot, and access control. The author concludes by calling for greater investment, education, and ecosystem building in IoT, particularly in South Korea, to catch up with global advancements. This post is valuable for anyone seeking a deeper understanding of IoT and its potential impact on various aspects of life and industry.